1. Field of the Invention
The present invention relates to a method for manufacturing an inkjet printing head, and particularly to a manufacturing technique of a power wiring for supplying drive power.
2. Description of the Related Art
An inkjet printing system utilizing a heating resistor (heater) is widely used because printing elements capable of realizing high drive frequency (ejection frequency) can be arranged in comparatively high density.
FIGS. 3A and 3B are a perspective view and a cross sectional view for explaining a general configuration of a printing head adopting such inkjet printing system. A heating resistor layer 205 forming heating resistors 205a to cause bubbles generated within ink, and wiring layers 201 and 202 performing electric connection to the heating resistor layer 205 are formed in high density on a substrate 200. Further, the substrate has a protective layer 206 for protecting the above wiring from the ink, and a heat storage layer 204 for storing heat. On the other hand, on a nozzle member 207, at a position corresponding to individual heating resistor 205a, a plurality of ink paths for leading the ink to a ejection opening 208 are formed in high density. A printing head is formed in such a way that the nozzle member 207 is adhered to the substrate 200 constituted as described above, in a condition as shown in FIG. 3A. Then, heat energy generated from the heating resistor causes the bubbles generated in the ink within the ink path, and the ink with an amount corresponding to a growing energy of the bubbles is ejected from the ejection opening 208.
For instance, Japanese Patent Laid-Open No. H06-286149 discloses a method for manufacturing a nozzle member provided with a plurality of ink paths arranged in high density and high accuracy. According to the present document, there is disclosed a manufacturing process in which, first, an ink path pattern is formed by using soluble resin, a covering resin including epoxy resin solid at ordinary temperature is applied to the ink path pattern, and the soluble resin layer is dissolved and eliminated after forming the ink ejection openings.
In addition, Japanese Patent Laid-Open No. H11-348290 discloses a method for bonding a covering resin being a nozzle member to a substrate on which a heating resistor and its wiring are formed in high density via an adhering layer made of a polyether amid resin.
Meanwhile, when referring to FIG. 3B, in such a substrate for inkjet printing head, a power wiring for supplying the drive power to the heating resistor 205a is formed with a two-layer structure of power wiring layers 201 and 202. Then, a current is led to the heating resistor 205a via a through hole part 203 formed on part of the two layers.
Conventionally, in such a power wiring layer, aluminum is frequently used. However, it is necessary to thicken an aluminum power wiring layer 201, or to thicken a width of an aluminum electrode wiring in the case of lowering a wiring resistance value. However, whichever method is used, since the substrate itself is made large, it is not appreciably to say a preferable method in manufacturing.
Compared with this, Japanese Patent Laid-Open No. 2006-210815 discloses a configuration in which gold (Au) having excellent characteristic as a wiring material with low current resistance is adopted as an electrode on the substrate. According to the document, a substrate manufacturing process is disclosed as being such that, by utilizing an electrolytic plating method, the gold (Au) as the electrode is formed on the substrate.
However, in the conventional substrate for the head in which the power wiring is formed by using electrolytic plating, battery reaction or the like accompanied by the difference of ionization tendency between different kinds of metals occurs, so that there are cases where corrosion or short-circuit of the power wiring is caused. Hereinafter, its cause will be described in detail.
In the conventional manufacturing process using the electrolytic plating method, a dry film formation is performed between a diffusion preventing material made of, for instance, TiW for performing foundation protection on a surface layer of the substrate, and gold of a foundation seed. In addition, in order to precipitate a metal wiring selectively by the electrolytic plating method, a photolithography technique is used. Further, with the metallic film formed as a mask, the above diffusion preventing material and gold of foundation seed are entirely etched by a dipping method. At this time, in the diffusion preventing layer, an etchant is introduced from also a lower side surface of the power wiring formed, and the side surface (cross section) is exposed by a side etching.
In the substrate for the inkjet printing head ejecting the ink being liquid, when the ink or the moisture or the like intrudes to part where the diffusion preventing material is exposed in such a way as above, the battery reaction accompanied by difference of ionization tendency between metallic material forming the diffusion preventing layer and the gold occurs. Then, this becomes cause of the corrosion or the short circuit of the power wiring.
Consequently, for instance, it is also possible to form an insulating inorganic film such as SiN by vacuum deposition so as to cover a cross-section surface of the diffusion preventing layer. However, it is difficult to perform the side etching uniformly in preferable condition to the lower side surface of the power wiring. When film thickness is thicken by the corresponding amount, thermal conductivity for the ink in the heating resistor decreases, and energy effect of the printing head itself becomes reduced.